How to export dataGridView data Instantly to Excel on button click?

I solved this by simple copy and paste method. I don't know it is the best way to do this but,for me it works good and almost instantaneously. Here is my code.

    private void copyAlltoClipboard()
    {
        dataGridView1.SelectAll();
        DataObject dataObj = dataGridView1.GetClipboardContent();
        if (dataObj != null)
            Clipboard.SetDataObject(dataObj);
    }
    private void button3_Click_1(object sender, EventArgs e)
    {
        copyAlltoClipboard();
        Microsoft.Office.Interop.Excel.Application xlexcel;
        Microsoft.Office.Interop.Excel.Workbook xlWorkBook;
        Microsoft.Office.Interop.Excel.Worksheet xlWorkSheet;
        object misValue = System.Reflection.Missing.Value;
        xlexcel = new Excel.Application();
        xlexcel.Visible = true;
        xlWorkBook = xlexcel.Workbooks.Add(misValue);
        xlWorkSheet = (Excel.Worksheet)xlWorkBook.Worksheets.get_Item(1);
        Excel.Range CR = (Excel.Range)xlWorkSheet.Cells[1, 1];
        CR.Select();
        xlWorkSheet.PasteSpecial(CR, Type.Missing, Type.Missing, Type.Missing, Type.Missing, Type.Missing, true);          
    }

Thanks.

using Excel = Microsoft.Office.Interop.Excel;


private void btnExportExcel_Click(object sender, EventArgs e)
{
    try
    {
        Microsoft.Office.Interop.Excel.Application excel = new Microsoft.Office.Interop.Excel.Application();
        excel.Visible = true;
        Microsoft.Office.Interop.Excel.Workbook workbook = excel.Workbooks.Add(System.Reflection.Missing.Value);
        Microsoft.Office.Interop.Excel.Worksheet sheet1 = (Microsoft.Office.Interop.Excel.Worksheet)workbook.Sheets[1];
        int StartCol = 1;
        int StartRow = 1;
        int j = 0, i = 0;

        //Write Headers
        for (j = 0; j < dgvSource.Columns.Count; j++)
        {
            Microsoft.Office.Interop.Excel.Range myRange = (Microsoft.Office.Interop.Excel.Range)sheet1.Cells[StartRow, StartCol + j];
            myRange.Value2 = dgvSource.Columns[j].HeaderText;
        }

        StartRow++;

        //Write datagridview content
        for (i = 0; i < dgvSource.Rows.Count; i++)
        {
            for (j = 0; j < dgvSource.Columns.Count; j++)
            {
                try
                {
                    Microsoft.Office.Interop.Excel.Range myRange = (Microsoft.Office.Interop.Excel.Range)sheet1.Cells[StartRow + i, StartCol + j];
                    myRange.Value2 = dgvSource[j, i].Value == null ? "" : dgvSource[j, i].Value;
                }
                catch
                {
                    ;
                }
            }
        }
    }
    catch (Exception ex)
    {
        MessageBox.Show(ex.ToString());
    }
}

This is a great question and I was surprised at how difficult it was to find a clear and complete answer, most of the answers I found were either sudo-code or not 100% complete.

I was able to create a complete solution to copy and save the data from my DataGridView to an excel file based on Jake's answer so I'm posting my complete solution in the hopes that it can help other new comers to c# like myself :)

First off, you will need the Microsoft.Office.Interop.Excel reference in your project. See MSDN on how to add it.

My Code:

using Excel = Microsoft.Office.Interop.Excel;

private void btnExportToExcel_Click(object sender, EventArgs e)
{
    SaveFileDialog sfd = new SaveFileDialog();
    sfd.Filter = "Excel Documents (*.xls)|*.xls";
    sfd.FileName = "Inventory_Adjustment_Export.xls";
    if (sfd.ShowDialog() == DialogResult.OK)
    {
        // Copy DataGridView results to clipboard
        copyAlltoClipboard();

        object misValue = System.Reflection.Missing.Value;
        Excel.Application xlexcel = new Excel.Application();

        xlexcel.DisplayAlerts = false; // Without this you will get two confirm overwrite prompts
        Excel.Workbook xlWorkBook = xlexcel.Workbooks.Add(misValue);
        Excel.Worksheet xlWorkSheet = (Excel.Worksheet)xlWorkBook.Worksheets.get_Item(1);

        // Format column D as text before pasting results, this was required for my data
        Excel.Range rng = xlWorkSheet.get_Range("D:D").Cells;
        rng.NumberFormat = "@";

        // Paste clipboard results to worksheet range
        Excel.Range CR = (Excel.Range)xlWorkSheet.Cells[1, 1];
        CR.Select();
        xlWorkSheet.PasteSpecial(CR, Type.Missing, Type.Missing, Type.Missing, Type.Missing, Type.Missing, true);

        // For some reason column A is always blank in the worksheet. ¯\_(ツ)_/¯
        // Delete blank column A and select cell A1
        Excel.Range delRng = xlWorkSheet.get_Range("A:A").Cells;
        delRng.Delete(Type.Missing);
        xlWorkSheet.get_Range("A1").Select();

        // Save the excel file under the captured location from the SaveFileDialog
        xlWorkBook.SaveAs(sfd.FileName, Excel.XlFileFormat.xlWorkbookNormal, misValue, misValue, misValue, misValue, Excel.XlSaveAsAccessMode.xlExclusive, misValue, misValue, misValue, misValue, misValue);
        xlexcel.DisplayAlerts = true;
        xlWorkBook.Close(true, misValue, misValue);
        xlexcel.Quit();

        releaseObject(xlWorkSheet);
        releaseObject(xlWorkBook);
        releaseObject(xlexcel);

        // Clear Clipboard and DataGridView selection
        Clipboard.Clear();
        dgvItems.ClearSelection();

        // Open the newly saved excel file
        if (File.Exists(sfd.FileName))
            System.Diagnostics.Process.Start(sfd.FileName);
    }
}

private void copyAlltoClipboard()
{
    dgvItems.SelectAll();
    DataObject dataObj = dgvItems.GetClipboardContent();
    if (dataObj != null)
        Clipboard.SetDataObject(dataObj);
}

private void releaseObject(object obj)
{
    try
    {
        System.Runtime.InteropServices.Marshal.ReleaseComObject(obj);
        obj = null;
    }
    catch (Exception ex)
    {
        obj = null;
        MessageBox.Show("Exception Occurred while releasing object " + ex.ToString());
    }
    finally
    {
        GC.Collect();
    }
}

I did not intend to steal @Jake and @Cornelius's answer, so i tried editing it. but it was rejected. Anyways, the only improvement I have to point out is about avoiding extra blank column in excel after paste. Adding one line dataGridView1.RowHeadersVisible = false; hides so called "Row Header" which appears on the left most part of DataGridView, and so it is not selected and copied to clipboard when you do dataGridView1.SelectAll();

private void copyAlltoClipboard()
    {
        //to remove the first blank column from datagridview
        dataGridView1.RowHeadersVisible = false;
        dataGridView1.SelectAll();
        DataObject dataObj = dataGridView1.GetClipboardContent();
        if (dataObj != null)
            Clipboard.SetDataObject(dataObj);
    }
    private void button3_Click_1(object sender, EventArgs e)
    {
        copyAlltoClipboard();
        Microsoft.Office.Interop.Excel.Application xlexcel;
        Microsoft.Office.Interop.Excel.Workbook xlWorkBook;
        Microsoft.Office.Interop.Excel.Worksheet xlWorkSheet;
        object misValue = System.Reflection.Missing.Value;
        xlexcel = new Excel.Application();
        xlexcel.Visible = true;
        xlWorkBook = xlexcel.Workbooks.Add(misValue);
        xlWorkSheet = (Excel.Worksheet)xlWorkBook.Worksheets.get_Item(1);
        Excel.Range CR = (Excel.Range)xlWorkSheet.Cells[1, 1];
        CR.Select();
        xlWorkSheet.PasteSpecial(CR, Type.Missing, Type.Missing, Type.Missing, Type.Missing, Type.Missing, true);          
    }